Wettable silicone hydrogel compositions and methods for their manufacture
||Wettable silicone hydrogel compositions and methods for their manufacture
||Lai, et al.
||January 23, 1996
||April 11, 1994
||Lai; Yu-Chin (Pittsford, NY)
Valint, Jr.; Paul L. (Pittsford, NY)
||Bausch & Lomb Incorporated (Rochester, NY)|
||Marquis; Melvyn I.
||Glass; Margaret W.
|Attorney Or Agent:
||Black; Edward W.Larson; Craig E.
||351/160H; 351/160R; 525/479; 526/279; 528/25; 528/26; 528/32; 528/41
|Field Of Search:
||525/479; 526/279; 351/16R; 351/16H; 528/32; 528/26; 528/41; 528/25
|U.S Patent Documents:
||3408429; 3496254; 4084459; 4136250; 4153641; 4197266; 4277595; 4343927; 4740533; 4810764; 4910277; 5034461; 5070215; 5310779; 5358995
|Foreign Patent Documents:
||Improved silicone-containing hydrogels are disclosed with enhanced wettability comprising a silicone-containing monomer, at least one acrylic-containing hydrophilic monomer, and at least one vinyl-containing hydrophilic monomer.
1. In a silicone-containing hydrogel composition formed by curing a monomer mixture comprising at least one silicone-containing monomer and a hydrophilic monomer, the improvement ofwhich comprises combining the silicone-containing monomer with N-vinylpyrrolidone and N,N-dimethylacrylamide in the monomer mixture.
2. The hydrogel of claim 1 wherein the weight ratio of N-vinylpyrrolidone to N,N-dimethylacrylamide present in the monomer mixture is from about 1:40 to about 40:1
3. The hydrogel of claim 1 wherein the combined weight percent of N-vinyl pyrrolidone and N,N-dimethyl acrylamide in the monomer mixture is from about 5 to about 80 weight percent.
4. The hydrogel of claim 1 wherein the combined weight percent of N-vinyl pyrrolidone and N,N-dimethyl acrylamide in the monomer mixture is from about 20 to about 60 weight percent of the polymeric hydrogel mixture.
5. The hydrogel of claim 1 wherein the Young's modulus of elasticity of the silicone containing hydrogel is from about 5 g/mm.sup.2 to about 400 g/mm.sup.2.
6. The hydrogel of claim 1 wherein the silicone-containing monomer is a polyorganosiloxane monomer.
7. The hydrogel of claim 1 wherein the silicone-containing monomer is an .alpha., .omega. bis(methacryloxyalkyl) dimethacrylate polysiloxane.
8. The hydrogel of claim 1 wherein the silicone-containing monomer is a bulky polysiloxanylalkyl (meth)acrylate monomer.
9. The hydrogel of claim 8 wherein the bulky polysiloxanylalkyl (meth)acrylate monomer is selected from the group consisting of methyloxypropyl tris(trimethylsiloxy) silane, pentamethyldisiloxanylmethylmethacrylate,tris(trimethylsiloxy)methacryloxy propylsilane, phenyltetramethyldisiloxanylethyl acrylate, and methyldi(trimethylsiloxy)methacryloxymethyl silane.
10. The hydrogel of claim 1 wherein the monomer mixture comprises N-vinylpyrrolidone, N,N-dimethylacrylamide and an .alpha., .omega. bis(methacryloxyalkyl)dimethacrylate polysiloxane.
11. In a contact lens formed from the polymerization product of a monomer mixture comprising at least one silicone-containing monomer and a hydrophilic monomer, the improvement of which comprises combining N-vinylpyrrolidone andN,N-dimethylacrylamide with the silicone-containing monomer in the monomer mixture.
12. The contact lens of claim 11 wherein the weight ratio of N-vinylpyrrolidone to N,N-dimethylacrylamide present is from about 1:40 to about 40:1.
13. The contact lens of claim 11 wherein the combined weight percent of N-vinyl pyrrolidone and N,N-dimethyl acrylamide in the monomer mixture is from about 5 to about 80 weight percent of the polymeric hydrogel mixture.
14. The contact lens of claim 11 wherein the combined weight percent of N-vinyl pyrrolidone and N,N-dimethyl acrylamide in the monomer mixture is from about 20 to about 60 weight percent of the polymeric hydrogel mixture.
15. The contact lens of claim 11 wherein the Young's modulus of elasticity is from about 5 g/mm.sup.2 to about 400 g/mm.sup.2.
16. The contact lens of claim 11 comprising N-vinylpyrrolidone, N,N-dimethylacrylamide and an .alpha., .omega. bis(methacryloxyalkyl)dimethacrylate polysiloxane.
||BACKGROUND OF THEINVENTION
1. Field of the Invention
The present invention relates to improved wettable polymeric hydrogel compositions useful for the production of biomedical devices, especially contact lenses.
Hydrogels have been a desirable class of material for the preparation of biomedical devices, and have been known since at least Wichterle, et al U.S. Pat. No. 3,220,960 which disclosed hydrogels comprising a hydrated polymer of a hydroxyalkylacrylate or methacrylate crosslinked with a corresponding diester (poly 2-hydroxyethyl methacrylate, known as poly-HEMA).
A hydrogel is a hydrated crosslinked polymeric system that contains water in an equilibrium state. The physical properties of hydrogels can vary widely and are mostly determined by their water content. Since hydrogels exhibit excellentbiocompatibility, there has been extensive interest in the use of hydrogels for biomedical devices, especially contact lenses.
In the field of contact lenses, various factors must combine to yield a material that has appropriate characteristics. Oxygen permeability, wettability, material strength and stability are but a few of the factors which must be carefullybalanced to achieve a useable end-result contact lens. Since the cornea receives its oxygen supply exclusively from contact with the atmosphere, good oxygen permeability is a critical characteristic for any contact lens material.
It was discovered that certain crosslinked polymeric materials could be hydrated and retain their water content. It was further found that the higher the water content within contact lenses made from these crosslinked hydrogel polymers, thegreater was the oxygen permeability through the lens to the cornea.
High water-containing hydrogels have at times exhibited undesirable mechanical properties. For example, such hydrogels are often not easily formed into hydrolytically stable lenses. Further such materials have at times exhibited tearing orother breakage as a result of poor tensile strength. What was needed was a highly oxygen permeable material that was durable and highly wettable. Wettability is important in that, if the lens is not sufficiently wettable, it does not remain lubricatedand therefore cannot be worn comfortably in the eye. The optimum contact lens would have not only excellent oxygen permeability, but also excellent tear fluid wettability.
Silicone-containing materials were tried as viable contact lens materials and displayed very good oxygen permeability and durability. However, most silicone-containing materials are largely hydrophobic and therefore not sufficiently wettable. Further, it is believed that such hydrophobicity causes enhanced deposit problems, which may also result in discomfort when wearing contact lenses made from certain silicone-containing polymers.
Therefore, an optimal hydrogel material for biomedical devices, such as contact lenses, would have ideal rigidity, high oxygen permeability and a high degree of wettability.
SUMMARY OF THE INVENTION
In accordance with this invention, the surface wettability of hydrogels, such as silicone-containing hydrogels, and more specifically polyurethane-silicone hydrogels and ethylenically terminated polysiloxane hydrogels such as (poly)organosiloxanehydrogels, are significantly enhanced by incorporating both at least one vinyl-containing hydrophilic monomer and at least one acrylic-containing hydrophilic monomer into the monomer mix along with the silicone-containing monomer or prepolymer.
Further, in accordance with the present invention, a method for making a wettable silicone-containing hydrogel composition is disclosed comprising the steps of a) combining at least one vinyl-containing monomer, at least one acrylic-containingmonomer and at least one silicone-containing monomer or prepolymer into a monomer mix and b) curing the monomer mix resulting from step a) to form a silicone-containing hydrogel composition.
It is believed that the combined vinyl-containing and acrylic-containing monomers act as wetting agents, and interact with the predominantly hydrophobic silicone-containing monomers and prepolymers in the monomer mix to produce highly wettablehydrogels with ideal rigidity. Such resultant hydrogels are especially well-suited for use as contact lens materials.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 depict the effect on modulus of polyurethane films as the composition ratio of NVP to DMA is changed.
FIG. 3 depicts the effect on modulus of methacrylate-capped polysiloxane films as the composition ratio of NVP to DMA is changed.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to improved wettability of hydrogels, especially silicone-containing hydrogels with ideal rigidity suitable for biomedical applications such as contact lenses.
The silicone-containing hydrogels of the present invention display improved wettability as a result of the combined presence in the monomer mix of at least one acrylic-containing monomer and at least one vinyl-containing monomer.
Silicone hydrogels (i.e., hydrogels containing silicone) are usually prepared by polymerizing a mixture containing at least one silicone-containing monomer and at least one hydrophilic monomer. Either the silicone-containing monomer or thehydrophilic monomer may function as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable fuctionalities) or a separate crosslinker may be employed.
The term "vinyl-containing" is meant to refer to non-acrylic monomers having the vinyl grouping (CH.sub.2 =CH--) which are generally highly reactive. Such vinyl groups are known to polymerize relatively easily. "Acrylic-containing" monomers arethose compounds containing the acrylic grouping (CH.sub.2 .dbd.CRCOX) which are also generally reactive.
The vinyl-containing monomers used in the present invention include hydrophilic monomers such as N-vinyl pyrrolidone, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl acetamide, N-vinyl-N-methyl formamide, N-vinyl formamide, with N-vinyl pyrrolidone(NVP) being the most preferred.
The acrylic-containing monomers used in the present invention include hydrophilic monomers such as 2-hydroxyethyl methacrylate, glycerol methacrylate, 2-hydroxyethyl methacrylamide, N,N-dimethyl (meth)acrylamide, diacetone acrylamide, methacrylicacid and acrylic acid with N,N-dimethylacrylamide (DMA) being the most preferred.
When both vinyl- and acrylic-containing monomers are present within one monomer mixture, it is preferable to add a crosslinking composition containing at least one vinyl-containing polymerizable group and at least one acrylic- orstyrene-containing polymerizable group disclosed in copending and commonly assigned U.S. application Ser. No. 07/788,071 filed Nov. 5, 1991 now U.S. Pat. No. 5,310,779 and having the following general schematic representation (I): ##STR1## R.sub.1,is an alkyl radical derived from substituted and unsubstituted hydrocarbons, polyalkylene oxide, poly(perfluoro) alkylene oxide, dialkyl-capped polydimethylsiloxane, dialkyl-capped polydimethylsiloxane modified with fluoroalkyl or fluoroether groups;
R.sub.2',-R.sub.10' are independently H, or alkyl of 1 to 5 carbon atoms;
Q is an organic group containing aromatic moieties having 6 to 30 carbon atoms;
X, Y, and Z are independently O, NH or S;
V' is 1, or higher; and
a', s' independently are greater than or equal to 0, and a'+s'.gtoreq.1.
The addition of crosslinking agents of Formula I assists in the copolymerization of the vinyl-and acrylic-containing monomers with each other as well as with other monomers and prepolymers present in the monomer mix, such as the relativelynon-polar ring-containing oxazolone compounds of the general formula (II): ##STR2## where R.sub.11 and R.sub.12 independently denote H or CH.sub.3; and
R.sub.13 and R.sub.14 independently denote methyl or cyclohexyl radicals.
These ring-containing monomers which may be incorporated into the silicone-containing hydrogels of the present invention specifically include 2-isopropenyl-4,4-dimethyl-2-oxazolin-5-one (IPDMO), 2-vinyl-4,4-dimethyl-2-oxazolin-5-one (VDMO),cyclohexane spiro-4'-(2'isopropenyl-2'-oxazol-5'-one) (IPCO), cyclohexane-spiro-4'-(2'-vinyl-2'oxazol-5'-one) (VCO), and 2-(-1-propenyl)-4,4-dimethyl-oxazol-5-one (PDMO). The preferred oxazolones are prepared by known reaction sequences set forth incommonly assigned U.S. Pat. No. 4,810,764. The amount of crosslinker used is about 0.01 to about 5% of the vinyl-containing monomer weight present in a useful formulation.
We have observed that silicone-containing hydrogels containing NVP as a wetting agent have a much higher modulus as compared with silicone hydrogels that incorporate acrylic-containing monomers, such as glycerol methacrylate and,N,N-dimethylacrylamide (DMA). We observed, and this invention contemplates, that the incorporation of a vinyl-containing hydrophilic monomer with an acrylic-containing hydrophilic monomer as wetting agents into silicone-containing formulations resultsin hydrogels suitable for biomedical applications, especially contact lenses.
Any known silicone-containing prepolymer may be used to form the silicone hydrogels of this invention, as will be apparent to one skilled in the art. The monomers added to the monomeric mixture may be monomers or prepolymers. A "prepolymer" isa reaction intermediate polymer of medium molecular weight having polymerizable groups. Thus it is understood that the terms "silicone-containing monomers" and "hydrophilic monomers" include prepolymers. Examples of such monomers may be found in U.S. Pat. Nos. 4,136,250; 4,153,641; 4,740,533; 5,034,461; and 5,070,215.
Further, notations such as "(meth)acrylate or " (meth)acrylamide are used herein to denote optional methyl sunstitution. Thus, for example, methyl (meth)acrylate includes both methyl acrylate and methyl methacrylate and N-alkyl (meth)acrylamideincludes both N-alkyl acrylamide and N-alkyl methacrylamide.
One preferred class of suitable silicone-containing monomers are bulky polysiloxanylalkyl (meth)acrylic monomers represented by the formula (III): ##STR3## wherein: X is O or NR;
each R is independently hydrogen or methyl; and
each R.sup.1 is independently a lower alkyl or phenyl group; and
f is 1 or 3 to 10.
Such bulky monomers include methacryloxypropyl tris(trimethylsiloxy)silane, pentamethyldisiloxanylmethylmethacrylate, tris(trimethylsiloxy)methacryloxy propylsilane, phenyltetramethyldisiloxanylethyl acrylate, andmethyldi(trimethylsiloxy)methacryloxymethyl silane.
A further preferred class of silicone-containing monomers are the poly(organosiloxane) prepolymers represented by the formula (IV): ##STR4## wherein: A is an activated unsaturated group, such as an ester or amide of an acrylic or a methacrylicacid;
each R.sup.3 -R.sup.6 is independently selected from the group consisting of a monovalent hydrocarbon radical or a halogen substituted monovalent hydrocarbon radical having 1 to 18 carbon atoms which may have ether linkages between carbon atoms;
R.sup.7 is a divalent hydrocarbon radical having from 1 to 22 carbon atoms; and
n is 0 or an integer greater than or equal to 1.
A further preferred class of silicone-containing monomers are the monomers having the following schematic representations:
(V) E(*D*A"*D*G).sub.a *D*A"*D*E'; or
(VI) E(*D*G*D*A").sub.a *D*G*D*E';
D denotes an alkyl diradical, an alkyl cycloalkyl diradical, a cycloalkyl diradical, an aryl diradical or an alkylaryl diradical having 6 to 30 carbon atoms;
G denotes an alkyl diradical, a cycloalkyl diradical, an alkyl cycloalkyl diradical, an aryl diradical or an alkylaryl diradical having 1 to 40 carbon atoms and which may contain ether, thio or amine linkages in the main chain;
* denotes a urethane or ureido linkage;
a is at least 1;
A" denotes a divalent polymeric radical of formula (VII): ##STR5## wherein: R.sup.s and R.sup.s' independently denote an alkyl or fluoro-substituted alkyl group having 1 to 10 carbon atoms which may contain ether linkages between carbon atoms;
m is at least 1; and
p provides a moiety weight of 400 to 10,000;
E and E' independently denote a polymerizable unsaturated organic radical represented by formula (VIII): ##STR6## wherein: R.sup.14 denotes a divalent alkylene radical having 1 to 10 carbon atoms;
R.sup.12 denotes H or CH.sub.3 ;
R.sup.13 denotes H, a (C.sub.1 -C.sub.6) alkyl radical or a --CO--Y--R.sup.15 group wherein Y is --O--, --S--or --NH--and R.sup.15 is a alkyl radical having 1 to 12 carbon atoms;
X is --CO--or --OCO--;
Z is --O--or --NH--;
Ar denotes an aromatic radical having 6 to 30 carbon atoms;
w is 0to 6;
x is 0 or 1;
y is 0 or 1; and
z is 0 or 1.
A preferred urethane monomer is represented by formula (IX): ##STR7## wherein: R.sup.16 is a diradical of a diisocyanate after removal of the isocyanate group, and is most preferably the diradical of isophorone diisocyanate, and m, p and a arethe same as previously defined. Preferably, the sum of m and a is 3 or 4, and more preferably, a is 1 and m is 3 or 4. Preferably, p is at least 30.
The wettable silicone-containing hydrogels of the present invention, when used in contact lens applications, can produce a wide variety of types of hydrogel contact lenses. As is understood in the field, in general, hydrogel contact lensesshould have oxygen permeabilities with DK values greater than about 20.times.10.sup.-11 cm.sup.3 .times.cm/sec.times.cm.sup.2 .times.mmHg (or 20 DK units) and preferably greater than about 60 DK. They should have a Young's modulus of elasticity in therange of about 5 to 400 g/mm.sup.2, preferably greater than about 20 g/mm.sup.2 as measured by ASTM test method D1938. Their water content should be between about 10 and 80 %, and preferably between 20 and 60%. The contact angle, which is a measurementof the wettability of the lens, should be less than about 80 degrees and should preferably be-less than about 40 degrees.
The preferred range of the combined vinyl-containing and acrylic-containing hydrophilic wetting monomer concentration is from about 5 weight percent of the polymeric hydrogel mix to about 80 weight percent, and more preferably from about 20weight percent to about 60 weight percent. The weight ratio of vinyl-containing monomer to acrylic-containing monomer is from about 40:1 to about 1:40, and is preferably higher than 1:1.
The present invention further provides articles of manufacture which can be used for biomedical devices, such as, contact lenses, surgical devices, heart valves, vessel substitutes, intrauterine devices, membranes and other films, diaphragms,surgical implants, blood vessels, artificial ureters, artificial breast tissue and membranes intended to come into contact with body fluid outside of the body, e.g., membranes for kidney dialysis and heart/lung machines and the like, catheters, mouthguards, denture liners, intraocular devices, and especially contact lenses.
It is known that blood, for example, is readily and rapidly damaged when it comes into contact with artificial surfaces. The design of a synthetic surface which is antithrombogenic and nonhemolytic to blood is necessary for prostheses anddevices used with blood.
The terms "shaped articles for use in biomedical applications" or "biomedical devices" mean the materials disclosed herein have physicochemical properties rendering them suitable for prolonged contact with living tissue, blood and the mucousmembranes.
Although the exact mechanisms are not fully understood at the present time, the wetting agents of the present invention appear to reduce the deposition problems normally associated with, and believed to be caused by, the high hydrophobicity ofthe hydrophobic silicone-containing monomers.
Further, the wetting agents of the present invention significantly reduce the contact angle of the surface--a clear indication to those skilled in the field that enhanced wetting has occurred. The resulting novel hydrogels comprising the wettingagents of the present invention were unexpectedly hydrolytically stable, within an acceptable range, while collecting only an acceptable level of deposits.
Two preferred classes of silicone-containing monomers contemplated by the present invention are urethane-containing prepolymers, and ethylenically terminated polysiloxane containing monomers as previously described herein, such as, mostpreferably .alpha.,.omega. bis(methacryloxyalkyl)polysiloxane.
The resulting polymers and copolymers disclosed herein can be boiled and/or autoclaved in water without being damaged whereby sterilization may be achieved. Thus, an article formed from the disclosed polymers and copolymers may be used, forexample, in surgery where an article is needed which is compatible with living tissue or with the mucous membranes.
The monomer mixes employed in this invention, can be readily cured to cast shapes by conventional methods such as UV polymerization, or thermal polymerization, or combinations thereof, as commonly used in polymerizing ethylenically unsaturatedcompounds. Representative free radical thermal polymerization initiators are organic peroxides, such as acetal peroxide, lauroyl peroxide, decanoyl peroxide, stearoyl peroxide, benzoyl peroxide. tertiarybutyl peroxypivalate, peroxydicarbonate, and thelike, employed in a concentration of about 0.01 to 1 percent by weight of the total monomer mixture. Representative UV initiators are those known in the field such as, benzoin methyl ether, benzoin ethyl ether, Darocure 1173, 1164, 2273, 1116, 2959,3331 (EM Industries) and Igracure 651 and 184 (Ciba-Geigy).
Polymerization of the monomer mix of this invention may be performed in the presence of a diluent. The polymerization product will then be in the form of a gel. If the diluent is nonaqueous, the diluent must be removed from the gel and replacedwith water through the use of extraction and hydration protocols well known to those skilled in the art.
It is also possible to perform the polymerization in the absence of diluent to produce a xerogel. These xerogels may then be hydrated to form the hydrogels as is well known in the art.
In addition to the above-mentioned polymerization initiators, the copolymer of the present invention may also include other monomers as will be apparent to one skilled in the art. For example, the monomer mix may include additional hydrophilicmonomers, colorants, curing agents, or UV-absorbing and toughening agents such as those known in the contact lens art.
The polymers of this invention can be formed into contact lenses by spincasting processes (such as those disclosed in U.S. Pat. Nos. 3,408,429 and 3,496,254), cast molding processes (such as those disclosed in U.S. Pat. Nos. 4,084,459 and4,197,266), combinations of methods thereof, or any other known method for making contact lenses. Polymerization may be conducted either in a spinning mold, or a stationary mold corresponding to a desired contact lens shape. The lens may be furthersubjected to mechanical finishing, as occasion demands. Polymerization may also be conducted in an appropriate mold or vessel to form buttons, plates or rods, which may then be processed (e.g., cut or polished via lathe or laser) to give a contact lenshaving a desired shape.
The hydrogels the present invention are oxygen transporting, hydrolytically stable, biologically inert, and transparent. The monomers and prepolymers employed in accordance with this invention, are readily polymerized to form three dimensionalnetworks which permit the transport of oxygen and are optically clear, strong and hydrophilic.
The relative softness or hardness of the contact lenses fabricated from the resulting polymer of this invention can be varied by deceasing or increasing the molecular weight of the polysiloxane prepolymer end-capped with the activated unsaturatedgroup or by varying the percent of the comonomer. As the ratio of polysiloxane units to end-cap units increases, the softness of the material increases.
The following examples serve only to further illustrate aspects of the present invention and should not be construed as limiting the invention.
The following abbreviations are defined as follows:
______________________________________ NVP is N-vinyl pyrrolidone DMA is N,N-dimethyl acrylamide HEMAVc is methacryloxyethyl vinyl carbonate TRIS is methacryloxypropyl tris(trimethylsiloxy)silane IDS3H is a urethane prepolymer derived from isophorone diisocyante, diethylene glycol, polysiloxanediol encapped with 2- hydroxyethyl methacrylate M.sub.2 D.sub.x is an a,x-bis(methacryloxyalkyl)- polysiloxane VDMO is 2-vinyl-4,4-dimethyl-2-oxazoline-5-one ______________________________________
Six polyurethane hydrogel films containing the following ingredients, were prepared:
a) IDS3H, 30 parts;
b) TRIS, 30 parts;
c) NVP, varied from 0 to 40 parts;
d) DMA, varied from 40 to 0 parts (NVP+DMA=40parts)
e) Methacryloxyethylvinyl carbonate (HEMAVc crosslinker) at 0.3% of NVP amount;
f) n-Hexanol 40 parts;
g) Darocur-1173, (UV initiator), 0.2 part.
These formulations were UV cured, followed by ethanol extraction and boiling water hydration, as is known in the art, to give resultant hydrogel films with the following properties (water content and modulus). FIG. 1 depicts the resultant filmsof Examples 1-6 with one plotted point for each film respectively.
TABLE 1 ______________________________________ EXAMPLE 1 2 3 4 5 6 ______________________________________ NVP/DMA ratio 40/0 38/2 35/5 30/10 20/20 0/40 % water 35 46 44 41 41 37 Modulus 430 281 150 80 79 63 ______________________________________
The modulus/composition relationship is depicted in FIG. 1.
A formulation was prepared containing the same ingredients and same weight ratios as those in Example 4, except that 3 parts of NVP and 1 part of DMA was replaced by 1 part of VDMO. The formulation was cast onto films and processed as done inExamples 1-6. The resulting hydrogel films had the following properties: water content, 40%; modulus 110 g/mm.sup.2.
Polyurethane formulations of the ingredients as in Examples 1-6 but of different relative parts, as shown in Table 2, were prepared.
a) IDS3H & b) TRIS, 34 parts each;
c) NVP & d) DMA, 32 parts combined;
e) n-Hexanol, f) HEMAVc and g) Darocure-1173, same parts as in Examples 1-6.
The formulations were cast and processed in the same manner as in Examples 1-6, with the water content and modulus data shown in Table 2. FIG. 2 depicts the resultant films of Examples 8-11, with one plotted point representing each filmrespectively.
TABLE 2 ______________________________________ EXAMPLE 8 9 10 11 ______________________________________ NVP/DMA ratio 32/0 24/8 16/16 0/32 water % 25 26 31 25 Modulus 610 275 107 87 ______________________________________
The modulus/composition relationship is further shown in FIG. 2.
M.sub.2 D.sub.x -based Hydrogel Films
The following silicone hydrogel formulations were prepared and cast processed into hydrogel films by the procedure of Examples 8-11. FIG. 3 depicts the resultant films of Examples 8-11, with one plotted point representing each film respectively. The ingredients in the formulation were:
a ) M.sub.2 D.sub.x, 13 parts
b) TRIS, 47 parts
c) NVP & d) DMA, 40 parts combined
e ) n-Hexanol, 40 parts
f) HEMAVc, 0.3 part of NVP amount
g) Darocur, 0.2 part
The modulus-composition relationship is depicted in FIG. 3.
Hydrogel Lens Casting
A monomer mix of the formulation as described in Examples 4, 9, 12 was filtered through a disposable 1.2 micron millipore filter into a clean vial. Under an inert nitrogen atmosphere, 60-90 ul of the mix was injected onto a clean plastic moldhalf and then covered with a second plastic mold half. The molds were then compressed and cured for 90 minutes in the presence of UV light (4200 microwatts/cm.sup.2). The molds were then opened mechanically and put into a beaker containing aqueousethanol. The lenses were released from the molds within 1 hour, then extracted with ethanol for 48 hours, and boiled in distilled water for 4 hours. The resultant lenses were inspected for cosmetic quality, cytotoxicity and dimensions. Lenses passinginspection were thermally disinfected in phosphate buffered saline prior to on-eye evaluation.
The cast-molded polyurethane lenses described in Example 12 were evaluated on six to ten patients. In each test, a poly (HEMA) control lens was worn on one eye and the test lens on the other eye. The lenses were analyzed after a minimum of onehour, and preferably 5 hours or longer for wettability and surface deposition study. The surface wettability rating scale was 0-4 with 0 representing 2/3 of the anterior surface unwetted by the tear film, and 4 representing complete wetting. Thedeposition scale was also 0-4 with 0 representing no surface deposits and 4 representing multiple deposits of 0.5 mm diameter or larger. The results for the lenses of the control formulation (according to Example 4) was 3.0 for wetting and 0.4 fordeposits after five hours of wear. For lenses comprising 1 part of VDMO (Example 7 formulation), the results showed a wettability rating of 3.3 and a deposit rating of 0.7 after 5 hours or wear.
Many other modifications and variations of the present invention are possible to the skilled practitioner in the field in light of the teachings herein. It is therefore understood that, within the scope of the claims, the present invention canbe practiced other than as herein specifically described.
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